Universal mobile telecommunications system (UMTS) is a 3rd Generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
The 3GPP LTE is a technology for enabling high-speed packet communications. Many schemes have been proposed for the LTE objective including those that aim to reduce user and provider costs, improve service quality, and expand and improve coverage and system capacity. The 3G LTE requires reduced cost per bit, increased service availability, flexible use of a frequency band, a simple structure, an open interface, and adequate power consumption of a terminal as an upper-level requirement.
FIG. 1 is a network structure of the E-UMTS, a mobile communication system applicable to the related art and the present invention.
With reference to FIG. 1, the E-UMTS network includes an E-UTRAN and an EPC (Evolved Packet Core). An interface between the E-UTRAN and the EPC can be used. An S1 interface can be used between the eNodeBs and the EPC. The eNodeBs are connected with each other through an X2 interface, and the X2 interface may be present between adjacent eNodeBs in a meshed network structure.
FIGS. 2 and 3 are block diagrams depicting the user-plane protocol and the control-plane protocol stack for the E-UMTS. As illustrated, the protocol layers may be divided into a first layer (L1), a second layer (L2) and a third layer (L3) based upon the three lower layers of an open system interconnection (OSI) standard model that is well known in the art of communication systems.
The physical layer, the first layer (L1), provides an information transmission service to an upper layer by using a physical channel. The physical layer is connected with a medium access control (MAC) layer located at a higher level through a transport channel, and data between the MAC layer and the physical layer is transferred via the transport channel. Between different physical layers, namely, between physical layers of a transmission side and a reception side, data is transferred via the physical channel.
The MAC layer of Layer 2 (L2) provides services to a radio link control (RLC) layer (which is a higher layer) via a logical channel. The RLC layer of Layer 2 (L2) supports the transmission of data with reliability. It should be noted that the RLC layer illustrated in FIGS. 2 and 3 is depicted because if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself is not required. The PDCP layer of Layer 2 (L2) performs a header compression function that reduces unnecessary control information such that data being transmitted by employing Internet protocol (IP) packets, such as IPv4 or IPv6, can be efficiently sent over a radio (wireless) interface that has a relatively small bandwidth.
A radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls logical channels, transport channels and the physical channels in relation to the establishment, reconfiguration, and release of the radio bearers (RBs). Here, the RB signifies a service provided by the second layer (L2) for data transmission between the terminal and the UTRAN. Voice information generated through an AMR (Adaptive Multi-Rate) codec (3GPP audio codec), namely, a voice codec used for a general voice call has special characteristics. The voice data include two types of patterns. A first pattern includes an interval during which a user actually talks, namely, a talk spurt, and a second pattern includes an interval during which the user does not speak, namely, a silent period. In general, voice packets including the voice information are generated at every 20 ms during the talk spurt, and the silent packets (SIDs) including the voice information is generated at every 160 ms during the silent period.
In addition, the ARM codec used for the voice call includes various modes and each mode is discriminated by the amount of data of the voice information. If the voice AMR codec operates in a mode, the AMR codec entity generates voice information of a certain size at certain time intervals. Thus, unless the mode of the AMR codec is changed, the size of the voice information packets delivered from an upper end (upper layer, upper stage) to a radio protocol entity is uniform (regular).
FIG. 4 shows the format of an RLC PDU used for an RLC entity. As shown in FIG. 4, an E-field informs whether information such as an LI (Length Indicator) is additionally added or not later. An SN field informs a sequence number of a corresponding PDU (Protocol Data Unit). An SI field informs whether a first byte of an included first SDU (Service Data Unit) is the same as a first byte of a data field of the PDU, or whether a final byte of the included final SDU is the same as a final byte of the data field of the PDU.
Here, the RLC functions to segments and re-combines RLC SDUs received from an upper layer to generate RLC PDUs, and re-assembles RLC PDUs received from a lower layer to restore RIC SDUs. Thus, a header of each RLC PDU includes re-combination information for segmentation or assembling, namely, segmentation information. Namely, all the SI, SN, E, and LI as described above can be the segmentation information.
FIG. 5 shows the format of a PDU used in the MAC entity. In FIG. 5, an LCID informs to which logical channel, an MAC SDU corresponds, and the field ‘L’ informs about the size of a corresponding MAC SDU. The field ‘E’ informs whether additional headers exist.
As described above, the packet information generated for the voice call communication has a certain characteristic. Namely, a voice packet generated from the voice call is created with a fixed size during a fixed time interval. In particular, since the voice packet is generated at every 20 ms and voice information is sensitive to a transmission delay, the terminal or the base station must process the voice packet immediately when it arrives, such that the voice packet can be processed before a next voice packet arrives. Usually, in this case, since only one voice packet exists in the receiving side at every interval, the receiving side does not need to perform any re-ordering process for a preceding packet or a subsequent packet nor to perform any special operation. Notwithstanding, in the conventional RLC PDU format, a sequence number is added to every RLC PDU. In addition, in most cases, only one voice packet is generated at every interval, and a single RLC PDU includes such voice packet. Thus, the information of LI (Length indicator) should not be included at the most time intervals. However, in the conventional RLC PDU format, the information of LI has to be included in the RLC PDU, thereby increasing the overhead of the RLC PDU.